A motor, such as a switched reluctance (SR) motor, is used to generate a mechanical power in response to an electrical input from a power source. Often times, the motor needs to be coupled to a power grid, such as a three-phase power grid, that provides electrical power to a large area. A motor system usually includes a motor driver that couples the motor to the power grid. The motor driver receives an input from the power grid and converts it to an electrical output that can be applied to the motor.
Some applications require that the motor operate at a variable speed. In such scenarios, the motor driver may need to be able to handle a peak voltage from the power grid. Power grids in different areas may have different voltage levels, and some power grids may have a grid voltage (effective voltage) higher than 500 V. For example, the grid voltage of a power grid may be as high as about 1000 V. The peak voltage of such a power grid is about 1400 V. Therefore, for a motor system coupled to such a power grid, the motor driver needs to be able to handle a voltage of about 1400 V.
One approach to achieve this purpose is to use higher voltage rated semiconductor devices, motor insulation systems, and other electric components that can function under the high voltage. However, such components usually cost more and have larger physical sizes. As a result, the motor also requires a more expensive insulation system, and has a higher construction cost and larger physical size.
U.S. Pat. No. 7,859,212 (the '212 patent) that issued to Pan et al. on Dec. 28, 2010, discloses a motor drive system with redundancy to compensate for possible failure in one or more of the inverters. When one of the inverters fails, either the other inverters increase output power to compensate for the power reduction due to such failure or a spare inverter is connected into the system.
However, in the system of the '212 patent, each inverter still operates under the full voltage of the power source. Therefore, the components in the system still need to be able to sustain the high voltage if the power source supplies a high voltage as described above.
The disclosed system is directed to overcoming one or more of the problems set forth above.